This invention relates to methods and apparatus for forming a combined image signal from a plurality of image signals representative of a plurality of images, and more particularly, to methods and apparatus for forming a combined image signal in which the density differences at the interface of the combined images are smoothed.
In the art of printing and in various modes of display, the formation of a combined image by inserting or overlapping is carried out. However, when a relatively large difference exists between the density of the image pixel at the opposite sides of the interface between the images, it is often observed as if line information other than the image information exists at the interface, creating an awkward impression.
In order to eliminate the above undesirable effect, a smoothing process utilizing an electronic computer has heretofore been carried out. When an image of an aircraft parked on an apron in a first picture is combined with an image of sky with floating clouds in a second picture to obtain a combined image of an aircraft flying in the sky, a mask of 1 bit with a 1 level within the contour of the aircraft and a 0 level outside of the aircraft image is prepared from the image of the aircraft on the ground. This mask is used to determine where the image of the aircraft alone should be placed in the image of the sky, and the interface and its vicinity in the combined images is densitygradated along the contour of the aircraft image combined with the sky image by an averaging method or an interpolating method.
The above described steps are carried out by a layout scanner system (an image processing system using a computer), but in the conventional system the image information that is displayable on the color monitor which plays an important role in image processing, is limited by the capacity of the image memory. Therefore, massive image information is compressed or eliminated at intervals to be displayed on the color monitor for easy processing, and the information processed through the use of the eliminated information must be converted back to a source data (image information input from or ourput into a scanner). This conversion may be simple or may be difficult or impossible if the latter is the case, the source data is displayed on the color monitor, but the image memory cannot store all of the source data. Therefore the source data is divided into several sections so that they can be displayed on the color monitor. The previously described conventional smoothing method corresponds to the case where conversion into the source data is difficult. In the conventional method, 1 bit mask is used to carry out the averaging method and the interpolating method, it is not possible to include the data from both image in the density-gradated region.
Therefore, according to the conventional smoothing method the smoothing is carried out by dividing the source data of the combined image into several sections and displaying them on a color monitor several times, thus requiring an inconveniently long time.
Also, although the density of the pixel to which the smoothing process has been effected is smoothly corrected, the image information expressed by the density change is disadvantageously eliminated.